1. Field of the Invention
This invention generally relates to improvements in lamps, especially ultraviolet lamps used in water purifiers.
2. Description of Related Art
Ultraviolet water purifiers are known for disinfecting contaminated water for domestic or commercial use. Such purifiers include at least one lamp for emitting ultraviolet radiation into a chamber filled with contaminated water to kill microorganisms therein. In conventional manner, the lamp includes two electrodes spaced apart within an elongated arc tube containing a gas, particularly mercury vapor with or without additives. A pair of end caps are mounted at the ends of the tube. Each electrode is electrically connected to a respective pair of contacts or terminal pins. The lamp is typically inserted endwise into the water purifier. To simplify insertion, both pairs of pins are conveniently mounted on one of the end caps. When the electrodes are energized by voltage from an electrical power supply, an electrical discharge is initiated in the gas between the electrodes. This discharge reacts with a layer of a radiation-emitting material coated on an interior surface of the arc tube and causes ultraviolet radiation to be emitted from the lamp in a manner well known in the art.
Although generally satisfactory for its intended purpose, the known ultraviolet lamp construction used in water purifiers is disadvantageous when high voltages are applied across the electrodes. In the humid, moisture-laden environment of a water purifier, electrical arcing between the pairs of terminal pins sometimes occurs at supply voltages as low as 40 volts. Such arcing short-circuits the electrodes and reduces the working lifetime of the lamp, thereby leading to frequent lamp replacement.